Sail Power and Famous Birthdays

The world can be powered by wind, water and sun alone.

Mark Z. Jacobson

You’d think there would be a simple formula to calculate the power that a set of sails can generate in a a given amount of wind . But then you would be wrong. I did find the following after doing a little web search:

Wind of 7- 10 knots HP = 0.015 x sail area in square feetSeaSea has 18 HP
Wind of 11-16 knotsHP = 0.020 x sail area in square feetSeaSea has 24HP
Wind of 17-21 knots HP = 0.040 x sail area in square feetSeaSea has 48 HP
Wind of 22-27 knotsHP= 0.070 x sail area in square feetSeaSea has 84 HP

I also discovered that 10 knots of wind exerts 396 pounds-force on a stationary wall that has an area equal to that of SeaSea’s sails. I thought it would have been more. Yes pounds-force sounds weird but that’s to distinguish it from pounds, the weight and for that matter pounds, the currency . Imperial units can be super confusing when entering the world of physics. For those so inclined the above force amounts to 1760 Newtons. Sir Isaac, who sorted out the math, has the same birthdate as Jimmy Buffett making it all the more relevant to the island sailor.

If there was no friction to slow things down, applying those 1760 Newtons to SeaSea, or anything else with the same mass, would accelerate her at a rate of a little less than half of a foot per second per second. That translates to a 0 to 60 mph time of about 3 minutes and 11 seconds. Let the clock run, in the same frictionless world, and SeaSea will eventually reach the speed of light, where Einstein takes over for Newton . Albert’s birthday is, incidentally , the same as that of Billy Crystal, who has a great first name, and who probably knows someone who has been sailing.

Of course the above is over simplified and silly . There are too many variables. Friction exist, airfoils are not the same as flat walls , waves go up and down, fish fart, and seagulls squawk. Accurately calculating the horsepower generated from a set of sails is quite the challenge and probably futile, but if you really want to give it a go you might give this a look. Even here they are talking about force not power . Good Luck .

Update 7/9/2022 I found this online calculator : Sailpowercalc

Published by billtan

Striving to be a better boat .

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